A non-toxic method of controlling the noxious weed Striga, the bane of farmers in Africa's Sahel region.

Striga hermonthica

Background:

In 1991, a team of scientists funded by the International Development Research Centre found a promising way to control the noxious weed Striga. Researchers at McGill University, led by Dr. Alan Watson and Marie Ciotola of the McGill Biopesticide Research Laboratory, discovered a fungus (Fusarium oxysporum) in the soil in Mali that can suppress the weed's growth. In a pilot study, the fungus was grown on sorghum straw, then spread on farmers' fields at sowing time. It is not toxic to humans or to cereal crops and attacks Striga at an early growth stage, resulting in dramatically increased sorghum yields.

Field experiments were performed from 1994 to 1997 in 4 different locations in Mali with different climatic and soil conditions. The summary below describes the best performance obtained for each year.

Striga spreads rapidly in areas of low soil fertility and decreasing plant diversity, conditions often experienced by poor farmers in dryland zones. The African countries most affected are Burkina Faso, Cameroon, Mali, Nigeria, Sudan, and Togo. Should this approach to controlling Striga eventually be adopted by African farmers, it would complement concerted efforts to replenish declining soil fertility.

Implementation Status

Initial testing of the fungus in a laboratory and under field conditions used an inoculum of Fusarium oxysporum M12-4A grown on sorghum straw, or glumes. The straw, or glumes, were soaked overnight, drained, sterilized, and inoculated with Fusarium. The fungus was then grown at 28°C for seven days and applied as wet or partially dried straw.

Because this approach would prove too time-consuming for farmers, a fermentation process was developed to produce a dry form of inoculum that can be stored and applied directly to the field. Ongoing research will also explore ways to prolong the shelf life of the inoculum and simplify its application. The hope is that cottage industries will eventually be established to produce the dry inoculum for sale to farmers.

Future Outlook and Potential Impact

• Striga-infested fields of sorghum treated with the fungus have shown a 75-90% reduction in Striga infestations and yield increases of up to 100%.
   
• Field testing has been restricted to Mali where the fungus was originally collected but will soon be expanded to neighboring countries including Kenya.
   
• Use of this fungus to control Striga could dramatically increase cereal crop yields in sub-Saharan Africa, where almost 530 million people depend directly on the land for their living. This would potentially increase incomes, food security, and nutrition in a continent where food production has not kept pace with rapid population growth.
   
• Use of the fungus could reduce the demand for imported chemical herbicides, which pose a threat to the environment and human health.
   
• This project could ultimately reduce losses caused by Striga infestations in Africa, estimated at US $7 billion annually.

Prerequisites

The success of this project will depend on an effective technology transfer strategy and, most importantly, on involving local communities in all stages of production and utilization of this new tool. A low tech system for production of the inoculum at the village level has already been developed. Aspects of this technology are still being refined, such as the design of a lid for cooking pots so they can be used as pressure cookers for sterilization of media, as well as ways to provide agitation to the inoculum production mixture and options to produce, package and distribute starter cultures. Plans are also being considered for the creation of small regional enterprises and for the empowerment of women to form cooperatives to produce, distribute and sell the biocontrol.

Constraints

Two of the major hurdles to cross will be maintaining a high quality starter culture inoculum and establishing a distribution system that will reach remote areas.

Potential Users

Potential beneficiaries of this research are farmers whose cereal crops are affected by Striga, particularly in Burkina Faso, Cameroon, Mali, Nigeria, Sudan, and Togo. Farmers in Mali will be the first to benefit because the Fusarium fungus used to make the soil inoculate originated there. Its use could be expanded to any other country that wishes to test it.

Documentation:

Ciotola, M.; Watson, A.K.; Hallett, S.G. 1995. Discovery of an isolate of Fusarium oxysporum with potential to control Striga hermonthica in Africa. Weed Research 35 (4) 303-309.

Ciotola, M.; Hallett, S.G.; Watson, A.K. 1996. Impact of Fusarium oxysporum isolate M12-4A, upon seed germination of Striga hermonthica in vitro. Sixth International Parasitic Weed Symposium, pp. 871-875. Moreno, M.T., Cubero, J.I.; Berner D.; Joel, D.; Musselman, L.J.; Parker, C., eds. April 16-18, 1996, Cordoba, Spain.

Savard M.; Miller, J.D.; Ciotola, M.; Watson, A.K. 1997. Production of metabolites by a strain of Fusarium oxysporum used for Striga control in west Africa. Biocontrol Science and Technology (in press).

Fungus Fights Cereal Killer in Africa, IDRC Reports

Kenya: Sebastian fallows for striga weed control?

Ker, Andrew. Farming Systems in the African Savanna: A continent in crisis. IDRC Books.

Profile: Joseph Oryokot, crop scientists at the Serere Agricultural and Animal Production Research Institute (SAARI)

Weeds, Weed Control and Management, ICRISAT

Submitted by:

Dr. Alan K. Watson Agronomy, Plant Physiology, & Agroecology Division
IRRI (International Rice Research Institute)
MCPO Box 3127 Makati City 2171 Philippines
Tel: 63-2-845-0563
Fax: 63-2-891-1292
E-mail: a.watson@cgiar.org
IRRI is one of 16 centers supported by the CGIAR (Consultative Group on International Agricultural Research)

Marie Ciotola, Research Consultant
McGill Biopesticide Research Laboratory
McGill University
Ste-Anne-de-Bellevue, Quebec,CANADA H9X 3V9
Tel: (514) 398-7851, ext. 8746
Fax: (514) 398-7897
E-mail: cyk6@musica.mcgill.ca

Don Peden, Program Officer
International Development Research Centre
P.O. Box 8500, Ottawa, Ontario, CANADA K1G 3H9
Tel: (613) 23-6163, ext. 2449
Fax: (613) 567-7749
E-mail: dpeden@idrc.ca